Nodes within wireless networks may communicate with each other using one or more wireless channels. Adaptive techniques are sometimes employed to allow a wireless node to adapt or modify certain transmission parameters based on changing channel conditions. Limited channel state information, or a channel quality indicator, such as a Signal to Interference and Noise ratio or SINR or other indicator, may sometimes be measured at the receiving node and provided to the transmitting node to allow the transmitting node to vary one or more parameters. In some cases, however, more detailed channel state information may be useful to allow the node to perform precoding or pre-equalization or other processing or functions relating to data transmission. Each channel may include a (e.g., time-varying) frequency response or channel response, which may indicate the manner in which signals may be distorted or modified during transmission via the channel. This may include, for example, signal attenuation and/or phase changes for one or more frequencies within the channel. These amplitude and phase distortions may be different for different frequencies and may change over time.
Precoding or pre-equalization may involve, for example, coding or modifying data prior to transmission to compensate at the transmitter for the frequency-dependent fading or channel distortion during transmission, e.g., such that the data may arrive at the receiver in an undistorted or less distorted form, for example. Other examples of precoding techniques at the transmitter modify the data prior to transmission to send data streams to multiple nodes without or with reduced interference between the data streams. Other types of processing may be performed at a transmitter as well, as precoding or pre-equalizaiton is merely one example.
A channel quality indicator, such as a SINR value, provides valuable information. In some cases, it may be useful to obtain more detailed channel state information. Therefore, techniques are desirable to allow wireless nodes to obtain channel state information in wireless networks.